Catastrophic flooding from Hurricane Florence has spread across parts of the USA with roads cut off by the epic deluge and muddy river water swamping entire neighbourhoods miles inland.

The disruption was threatening both North and South Carolina with Wilmington and the surrounding area particularly badly affected on Sunday.

North Carolina governor Roy Cooper declared "the risk to life is rising with the angry waters" as the storm's death toll climbed to 17.

The storm continued to crawl westward, dumping more than 30 inches of rain in spots since Friday, and fears of historic flooding grew.

Tony Thompson was at his mobile home on Friday night when he says it exploded around him as Hurricane Florence moved inland over Newport, North Carolina (Image: SIPA USA/PA)

Oliver Kelly, one, is rescued in the aftermath of Hurricane Florence in Leland, North Carolina (Image: REUTERS)

Tens of thousands were ordered evacuated from communities along the state's steadily rising rivers - with the Cape Fear, Little River, Lumber, Waccamaw and Pee Dee rivers all projected to burst their banks.

In Wilmington, with roads leading in and out of the city underwater and streams still swelling upward, residents waited for hours outside stores and restaurants for basic necessities like water.

Police guarded the door of one store, and only 10 people were allowed inside at a time.

Woody White, chairman of the board of commissioners of New Hanover County, said officials were planning for food and water to be flown into the coastal city of nearly 120,000 people.

"Our roads are flooded," he said. "There is no access to Wilmington."

A boat sits in a backyard after the passing of Hurricane Florence in New Bern, North Carolina (Image: REUTERS)

About 70 miles away from the coast, residents near the Lumber River stepped from their homes directly into boats floating in their front yards; river forecasts showed the scene could be repeated in towns as far as 250 miles inland as waters rise for days.

Downgraded overnight to a tropical depression, Florence was still massive. But with radar showing parts of the storm over six Southeastern states and flood worries spreading into southern Virginia and West Virginia, North and South Carolina were still in the bull's-eye.

Dogs left caged by an owner who fled rising flood waters are freed by volunteer rescuer Ryan Nichols of Longview, Texas, in Leland, North Carolina (Image: REUTERS)

Half way around the world, meanwhile, Typhoon Mangkhut barreled into southern China on Sunday after lashing the Philippines with strong winds and heavy rain that left dozens dead.

More than 2.4 million people were evacuated from China's southern Guangdong province ahead of the massive typhoon, the strongest to hit the region in nearly two decades.

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In North Carolina, fears of what could be the worst flooding in the state's history led officials to order tens of thousands to evacuate, though it was not clear how many had fled or even could.

The head of the Federal Emergency Management Agency (Fema), Brock Long, said officials were focused on finding people and rescuing them.

A huge tree sits atop a home on Queens Road West in Charlotte, North Carolina (Image: SIPA USA/PA)

"We'll get through this. It'll be ugly, but we'll get through it," Mr Long told NBC's "Meet The Press."

President Donald Trump said federal emergency workers, first responders and law enforcement officials were "working really hard".

As the storm "begins to finally recede, they will kick into an even higher gear. Very Professional!" he declared in a tweet.

The storm's death toll climbed to at least 17 when a three-month-old child was killed when a tree fell across a mobile home in North Carolina.

Local resident Doug Erickson ducks under a felled pecan tree in front of his home in Wilmington, North Carolina (Image: SIPA USA/PA)

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Earlier, officials said three people died in separate, weather-related traffic accidents in South Carolina.

Victor Merlos was overjoyed to find a store open for business in Wilmington since he had about 20 relatives staying at his apartment, which still had power. He spent more than 500 dollars on cereal, eggs, soft drinks and other necessities, plus beer.

"I have everything I need for my whole family," said Mr Merlos.

Nearby, a Waffle House restaurant limited breakfast customers to one biscuit and one drink, all take-out, with the price of two dollars per item.

A pickup truck is submerged in floodwater in Lumberton, North Carolina (Image: AFP)

As rivers swelled, state regulators and environmental groups were monitoring the threat from gigantic hog and poultry farms located in low-lying, flood-prone areas.

The industrial-scale farms contain vast pits of animal faeces and urine that can pose a significant pollution threat if they are breached or inundated by floodwaters.

The Defence Department said about 13,500 military personnel had been assigned to help relief efforts.

Marcus Dipaola helps 5-year-old Ember Kelly off a rescue boat carrying her sisters and mother from rising flood waters in the aftermath of Hurricane Florence, in Leland, North Carolina (Image: REUTERS)

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Authorities ordered the immediate evacuation of up to 7,500 people living within a mile of a stretch of the Cape Fear River and the Little River, about 100 miles from the North Carolina coast.

Fayetteville city officials, meanwhile, got help from the Nebraska Task Force One search and rescue team to evacuate 140 residents of an assisted-living facility to a safer location at a church.

In Swansboro, North Carolina, nearly 34 inches of rain had fallen by Sunday afternoon and 20 other places in North Carolina had at least 20 inches, according to the National Weather Service. Another 30 sites in North and Carolina had at least 10 inches.

Flood waters from Hurricane Florence surround a house and flow along the street in Fayetteville, North Carolina (Image: Getty Images North America)

Water on the Cape Fear River near Chinquapin got so high that electronic instruments used to monitor flooding quit working after it became submerged, the US Geological Survey said.

Still, there was some good news as power outages in the Carolinas and Virginia were down to about 580,000 homes and businesses after reaching a high of about 910,000 as the hurricane ploughed into the coast. Utilities said some outages could last for weeks.